Decontamination of toxic gases through formation of gas hydrate

ABSTRACT

Areas in which toxic material has been released, particularly in gaseous form but also in liquid form, are decontaminated by forming gas hydrate of the toxic agent. Smaller-molecule toxic agents form sI or sII type hydrates, whereas larger-molecule toxic agents for sH type hydrates. A “companion gas” or “companion agent” is supplied to fill the smaller voids of the sH hydrate, thereby enabling larger-molecule toxic agents to form hydrates by filling the larger voids of the sH hydrate which, but for the presence of the smaller-molecule agent in the smaller voids, would be unstable and not form. Portable as well as fixed, permanently installed apparatus for conducting hydrate-based decontamination is also disclosed.

[0001] This Application is based on and claims the benefit ofProvisional Patent Application Nos. 60/329,316 filed Oct. 16, 2001, and60/354,248 filed Feb. 6, 2002, the entire contents of which are herebyincorporated by reference.

FIELD OF THE INVENTION

[0002] The invention relates to decontamination using gas hydrate tocapture toxic gas molecules and render them inert within solid gashydrate crystals.

BACKGROUND OF THE INVENTION

[0003] The United States now faces increased terrorist threats. Ofconcern is attack using toxic gases and/or liquids.

[0004] Beside terrorist attacks, other dangers involving toxic gasesexist. For example, certain gases and liquids that are available forindustrial use may be highly toxic. These and other gases that arecommercially and widely available are likely to be spilled in quantitieson the scale of large tanker trucks, either accidentally ordeliberately, well away from the industrial sites at which they arenormally handled (and where such spills ordinarily are attended to).

[0005] Decontamination of major spills of toxic gases is generallydifficult due to the chemical hazard presented (both to innocentbystanders as well as to decontamination personnel) and because thetoxic materials often are highly persistent and difficult to capture.Typically, it is believed, “clean-up” involves little more than dilutionof the toxic material, which is often simply washed or flushed awayrather than collected and disposed of safely because collecting toxicmaterial and concentrating it is difficult and dangerous.

[0006] In general, gas hydrate is a non-stochiometric mineral speciesthat forms from water and gas molecules. The crystalline structure is anopen network of water molecules, with voids containing the gasmolecules. The presence of the gas molecules stabilizes the watermolecule meshwork via van der Waals electrostatic bonding. The voids ingas hydrate usually are of different sizes, depending on the particulartype of gas hydrate species. Table 1 below shows examples of the voidsizes of the three most common types of naturally occurring hydrate,from which the size of the gas molecule that can form a particular typeof hydrate can be estimated. (Other types of hydrate species may havedifferent (i.e., smaller or larger) ranges of void size and/or differentnumbers of voids.) To determine the diameter of a gas molecule that maybe accommodated in a particular void, it may be necessary to subtractthe van der Waals radius of the water molecule (1.4 Å) from the averagecavity radius. TABLE 1 Hydrate Crystal Structure I (sI) II (sII) H (sH)Void Size Small Large Small Large Small Medium Large Description 5¹²5¹²6²  5¹² 5¹²6⁴ 5¹² 4³5⁶6³  5¹²6⁸ Number of 2 6 16 8 3 2  1Cavities/Unit Cell Average Cavity 7.90 8.66  7.82 9.46 7.82 8.12 11.42Diameter, Å

[0007] In addition to the geometric information shown in Table 1,pressure/temperature fields of stability for a wide variety of gashydrates are known, with the fields of stability for hydrate of somegases being more completely known than the fields of stability forhydrate of other gases. In general, the most information is known aboutsI gas hydrates, which include the relatively common methane hydrate(very widely distributed naturally on Earth) and carbon dioxide hydrate.Often (but not always) sII type hydrate will include more than one typeof gas.

[0008] Pressure/temperature fields of stability for various sH type gashydrates are also known, albeit comparatively imperfectly. (The term“sH” is used at the present time to describe gas hydrates in which thedimensions of the voids that house the gas molecules are stronglydifferent; it is likely that many species of hydrate that have yet to bedescribed will fall within this sH category.) For a given gas or mixtureof gases, however, it is known that sH gas hydrates will form undercertain pressure and temperature conditions, and the ability of a givengas or mixture of gases to form hydrate is widely and strongly believedto be a function of the size of the gas molecule. Table 2 below showsexamples of relatively large-molecule gases that are known to occupy thelarge void spaces of sH type gas hydrate. TABLE 2 Large Guest Diameter,Å Pressure, MPa Temperature, ° C. 2-Methylbutane 7.98 1.974 02,3-Dimethylbutane 7.99 1.439 0 2,2-Dimethylbutane 7.97 1.064 02,2-Dimethylpentane 9.25 2.140 0 3,3-Dimethylpentane 9.24 1.373 02,2,3-Trimethylbutane 8.00 0.959 0

[0009] (The pressure and temperature values are single-point data(rather than field data) at which hydrate of the guest gas molecule isstable.)

SUMMARY OF THE INVENTION

[0010] The present invention overcomes many limitations of the presentpractices for decontamination of various toxic gases by forming gashydrate using the toxic gas as, the hydrate-former and carrying out thisprocess of gas hydrate formation under controlled conditions that allowthe toxic gas to be captured safely and disposed of. Trapping toxic gasmolecules in the form of crystalline gas hydrate renders the gaseschemically non-reactive and essentially safe to handle.

[0011] Relatively small-diameter toxic gas molecules can form type sI ortype sII hydrate. In order to capture larger-molecule toxic gases inhydrate, which larger-molecule gases are too large to fill the voidswithin type sI or type sII hydrate, type sH hydrate is caused to beformed. Because the larger-molecule toxic gases are also too large tofill the smaller voids in the sH type hydrates, but are able to fill thelarger voids in the type sH hydrate, a “companion gas” or “companionagent” is provided. The companion gas or agent fills the smaller voidsin the type sH hydrate, and the larger-molecule toxic agent fills thelarger voids in the type sH hydrates. Presence of the companion agentrenders the hydrate crystals stable, thereby facilitating hydrate-baseddecontamination of larger-molecule toxic agents.

[0012] Once captured in gas hydrate, the toxic gas molecules arechemically unreactive and generally safe to handle. The toxic gasremains safe so long as the hydrate is maintained under conditions ofstability for the particular gas hydrate.

[0013] Specialized apparatus according to the invention is provided,which apparatus ingests air that has been polluted by toxic gas into ahydrate formation vessel that is pressurized and cooled (as required) sothat when water is introduced into the hydrate formation vessel, hydrateof the toxic gas will form spontaneously. Alternatively, the hydrateformation vessel may be filled with water and the toxic gas introducedinto the water-filled vessel to form hydrate. The toxic gas hydrate isthen concentrated and collected by allowing it to settle within thehydrate formation vessel.

[0014] A pressurized hydrate formation vessel or vessels utilize(s) awater spray in a pressurized environment in which thepressure/temperature regime is suitable for the formation of gas hydrateusing the toxic gas itself as the hydrate-forming agent. Water, which isobtained either from local sources or brought to the location, isbrought into contact with the toxic hydrate-forming gas-and-air mixturethat has been ingested into the apparatus so that solid gas hydrate willform and be concentrated. Thus, the hydrate-forming gas can beconcentrated and removed from the decontamination site in a safe andexpedient manner.

[0015] After the hydrate has been accumulated, thereby concentrating thetoxic gas, the water and the toxic gas can be separated by altering thepressure and/or temperature conditions under which the hydrate is heldto render the hydrate unstable, thus causing the toxic gas hydrate todissociate under controlled conditions. The toxic gas is released fromthe hydrate and recovered in a relatively pure and highly concentratedform—either pressurized or as a liquid, depending on thepressure/temperature characteristics of the particular toxichydrate-forming gases and on the desired nature of the product—thusminimizing the volume of toxic material to be handled. Water isrecovered and reused for further formation of toxic gas hydrate, thusminimizing the amount of water to be treated for dissolved toxic gas andother pollutants following successful completion of the decontaminationoperation.

[0016] Toxic gas hydrate decontamination units according to theinvention can be fixed or portable. In order for decontaminationapparatus to be used effectively, however, it must be employed at thepoint of use as rapidly as possible. Therefore, in a preferredembodiment, toxic gas hydrate decontamination units are highly portable.Thus, modular and highly portable apparatus is built into standardcontainers for free-standing or truck-mounted use with a minimum amountof site preparation required. The need for rapid set-up and deploymentis a result of the nature of chemical hazards, which tend to spread outover time and extend their toxicity over larger areas as a function oftheir expansion and dilution. Thus, the sooner decontamination apparatuscan be brought into use, the more effective it will be, since the toxicgas will be more concentrated and a smaller amount of mixed air willhave to be ingested and processed to capture the toxic gas. This willresult in faster decontamination and diminish the likelihood of damage.

[0017] In a preferred embodiment of portable hydrate-baseddecontamination apparatus, the toxic gas hydrate vessel constitutes notonly the pressurized container in which the toxic gas hydrate is formed,but also the collection and dissociation vessel. This has the benefit ofminimizing the number of containers in which the toxic gas and hydratemust be contained and of minimizing the chance of spillage when thetoxic gas hydrate is transferred from one vessel to another.

[0018] Theoretically, it should be possible to capture virtually everymolecule of the toxic gas that is present, assuming sufficient water canbe brought into the immediate vicinity of the gas molecules. That isbecause the gas molecules occupy lattice sites within the hydratecrystals, which have a water molecule framework; in the presence ofexcess water, thermodynamic principles drive every gas molecule to formhydrate within the field of stability for the particular gas hydrate.For certain toxic gases, single gas molecules can form basic cells ofgas hydrate. Thus, even very small quantities of toxic gas molecules canform toxic gas hydrate. In principle, in the presence of excess water,every toxic gas molecule can be captured in the form of solid hydrateand separated from the air with which it was brought into the hydrateformation vessel. This would result in treated air (and water) that isvirtually entirely decontaminated following extraction of the toxic gasmolecule from the air.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention will now be described in greater detail inconnection with the drawings, in which:

[0020]FIG. 1 is a diagrammatic perspective view of a first portableembodiment of hydrate-based decontamination apparatus according to theinvention that is configured for use in forming hydrate ofsmaller-molecule toxic agents;

[0021]FIG. 2 is a diagrammatic section view of a water drainage pipe foruse in the apparatus of FIG. 1 or FIG. 3;

[0022]FIG. 3 is a diagrammatic perspective view illustrating apermanently installed embodiment of hydrate-based decontaminationapparatus installed in a subway station according to the invention; and

[0023]FIG. 4 is a diagrammatic perspective view of a second portableembodiment of hydrate-based decontamination apparatus according to theinvention that is configured for use in forming hydrate oflarger-molecule toxic agents.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0024] According to one embodiment of the invention, certain toxic gaseshaving relatively small molecular diameters are captured by forming typesI or type sII hydrates to decontaminate an area in which such toxicagent has been released. In order to form a type sI or type sII hydrate,the molecules of the toxic agent must be less than about 7 Å in diameterin order to fit within the voids of the hydrate cage. Bromine (Br₂, 5.9Å), chlorine (Cl₂, 5.2 Å), hydrogen cyanide (HCN, 4.8 Å), and possiblyphosgene (CCl₂O, 6.1 Å) are examples of such hydrate-forming toxicagents which are amenable to decontamination via hydrate formation. Forexample, chlorine hydrate can form at temperatures up to slightly over25° C. and at pressures as low as only slightly higher than normalatmospheric pressure. Bromine is also known to form hydrate, althoughthe full temperature/pressure hydrate formation/stability region ofbromine is not completely known.

[0025] A toxic gas hydrate decontamination unit 100 by means of whichrelatively small-diameter toxic gas molecules can be converted tohydrate is illustrated in FIG. 1. The gas hydrate decontamination unit100 is relatively modular in design. The hydrate formation vessel 120 isa central component of the apparatus for capture and concentration ofthe toxic gas. Although the vessel 120 is illustrated as a continuous,open cylinder, this is for simplicity only. Actual hydrate formationvessels 120 may be formed from joined, linearly arranged sections; maybe concentrically arranged; or may have complex internal geometries tosatisfy particular area or volume requirements within the vessel.

[0026] In the illustrated embodiment, the vessel is also the locationfor processing the toxic gas hydrate so that the toxic gas can be safelyrecovered. In addition to rendering the toxic gas non-reactive andtherefore relatively safe, forming hydrate of the toxic gas alsocompresses it. Typically, in a type sI structure gas hydrate, there is acompression factor of about 160. In other words, for every volume of gasat standard pressure and temperature, about 160 volumes of gas can beheld within each volume of hydrate. (For larger molecule toxic gases,which form type sH hydrates as addressed below, the compression factoris calculated to be on the order of about 30.) This allows forrelatively low-pressure hydrate-formation vessels to contain volumes ofgas that would otherwise require much higher pressures to be contained,i.e., if the gas were simply to be compressed to a comparable volume.

[0027] Certain toxic gas hydrates such as (but not limited to) chlorineand bromine hydrate have been determined to be stable at pressures aslow as only two atmospheres above normal atmospheric pressure. Thelow-pressure nature of the hydrate formation vessel required to containsuch toxic gas hydrate allows it to be fabricated of relativelylight-weight material such as thin stainless steel, aluminum, orcomposite material, depending on the desired strength and chemicalreaction anticipated with the various species of toxic hydrate-forminggas. As a result, hydrate formation vessels will be relativelyinexpensive to fabricate and light enough to be highly portable byfixed-wing or rotary-wing (i.e., helicopter) aircraft to a contaminationsite.

[0028] An upstream component of the toxic gas hydrate decontaminationunit 100 is the intake assembly 108. This assembly includes one or moreflexible intake pipes 106 that can be connected so as to reachconsiderable distances into tunnels or buildings. These intake pipes 106are water- and air-proof and, in a preferred embodiment, are fabricatedfrom light-weight, strong synthetic fabric similar to modem parachutefabric. The shape of the pipe may be maintained by semi-rigid yetflexible helical plastic reinforcements. Such construction of the intakepipes 106 allows them to be very light-weight and to be folded into asmall space for transport. Deployment at the decontamination site israpid, with zipper of other waterproof fasteners being used to joinmultiple flexible intake pipe segments 106 together.

[0029] Following use, the intake pipes themselves will be contaminatedand must be safely contained and disposed of. Because of theirflexibility and ability to be folded into a small space, the used intakepipes are compressed into boxes or containers that provide for theirchemical hazard isolation, and they are then taken to specialdecontamination facilities for disposal.

[0030] The light weight and ease of assembly of the intake pipes 106enables them to be rapidly assembled and deployed from where the hydrateformation vessel 120 is located into the decontamination site, eitherremotely (by robot) or by suitably protected personnel. The intake pipesare connected to the housing of pump assembly 110 with quick-fitconnections such as flanges, bayonet fittings, or other inexpensive andeffective means for forming a joint. The intakes are extended into theimmediate vicinity of the contamination, and the contaminated air isingested by suction.

[0031] The toxic gas and atmospheric air are drawn into and slightlycompressed by the pump assembly 110 into an intermediate stage pressurevessel 114, which may be made of flexible, semi-rigid, or rigid (andtherefore much stronger) material, depending on the desired or requiredpressures for this region of the apparatus. The pumps in the assembly110 can be directly electrically driven or drivenhydraulically—whichever is safer and more expedient depending on factorssuch as the likelihood of igniting the toxic gas. The connection betweenthe pump assembly 110 and the intermediate stage pressure vessel 114 isalso a quick-change-type of fitting, which facilitates rapid initialset-up and provision of replacement modules as needed so thatdecontamination may proceed virtually uninterrupted even in the event ofequipment failure. An intake air chiller 118 may also be provided sothat the temperature inside the hydrate formation vessel is low enoughfor hydrate to form.

[0032] Exhaust system 140 ducts processed air away from the toxic gashydrate decontamination unit. The exhaust system can be relativelyshort, or it can be long enough for the treated air to be carried somedistance away. The fitting between the exhaust system 140 and thehydrate formation vessel 120 should also be of the quick-release type.If desired, a venturi assembly (not illustrated) can be provided in theexhaust system to mix exhaust gas with outside air to minimize moisturein the exhaust air stream. The exhaust gas will be at no greaterpressure or temperature than that of the interior of the hydrateformation vessel 120. No compensation for raising or loweringtemperature is necessary within the exhaust system, but provision forstep-down of pressure (e.g., an energy-recovering,electricity-generating turbine (not shown) in the exhaust stream) may beprovided.

[0033] Provision is also made to ensure that, taking into accountcompression from injecting the air-toxic gas stream, decompression ofthe gas as the hydrate forms, and the decompression as air from whichtoxic gas has been removed is released, formation of gas hydrate remainsrelatively continuous. To that end, gas flow through the system will notbe perfectly continuous, but rather, may be pulsed so that internalpressure will be cycled from lower to higher by opening and closingone-way valves (not shown) at the junctions 116 and 136 of the airintake system and the air exhaust system, respectively, with the hydrateformation vessel 120.

[0034] The water injection system used to introduce into the systemwater from which the hydrate forms consists of a water injection line124 and injectors 145, a recovery line 128, and collector pipes 146. Thepositioning of the injectors and collectors in FIG. 1 are not to scaleor in precise positions, but rather reflects the general elements of thesystem. Water is injected as a spray or fine vapor that allows foroptimum formation of gas hydrate from the air stream. The spray geometryand injection rate of the water can be varied by means of a variablespray valve inside the hydrate formation vessel or by insertingdifferent nozzles prior to start-up.

[0035] Water collection drain pipes 146 each have a series of drainageslots or holes in their sides and are surfaced with hydrophobic coatingsto retard the hydrate from adhering to them and clogging the water drainslots. The pipes protrude into the hydrate formation vessel 120 becauseit is expected that the hydrate formation vessel will become filled withgas hydrate and the permeability and porosity of hydrate in the lowerpart of the vessel may be such as not to permit surplus water to flowthrough the hydrate to exit through the water collection pipes.

[0036] A number of industrial gases form hydrate that is more dense thaneither fresh or saline water Excess water can be separated from hydrate,which will collect in the bottom 121 of the pressure vessel, by, forinstance, use of a water trap. In order to ensure that the watercollection drains in the sides of the water drain pipes 146 are blockedby hydrate formation as little as possible, they are preferably shroudedfrom above as illustrated in FIG. 2. Shrouded or hooded drain pipes 146each have an overlapping, upper shroud or hood 150 that extends belowthe actual slot or hole 152 in the drain pipe mouth, which allows water(W) to enter the drain pipe 146 and flow down the pipe after it hasseparated from the higher density gas hydrate (H). The hood is held inplace by internal braces 154. Hydrate (H) falls to the bottom 121 of thepressure vessel 120, where it accumulates and stratifies. Water exitsfrom the pressure vessel 120 through a non-return valve (not shown)located either in the drain pipe or outside of it. When the hydraterises to a level where no more water may be removed, the remaining wateris drained and the hydrate-filled vessel is removed from thecontaminated air-capture system and warmed so that the hydratedissociates into gas and water. The drain pipes may be telescoping (notillustrated) to allow water to drain while hydrate settles so that aminimal amount of water above the settled hydrate is removed, recycled,and reused for forming hydrate.

[0037] Where positively buoyant hydrates form from toxic gases, thehydrate naturally rises within the water and the water drains in thelower part of the pressure vessel 120 can be relatively simple, screeneddrains with little or no drain pipe extending above the bottom 121 ofthe vessel 120.

[0038] It is known that chlorine, which is the most widely available ofthe industrial toxic gases that presumably may be used by terrorists,forms negatively buoyant gas hydrate. In those cases, hydrate that formswill settle to the bottom 121 of the hydrate formation vessel 120. Inthe case of positively buoyant toxic gas hydrates, on the other hand,the relative position of the hydrate and the water within the vessel 120will be more complex, especially as water may not be drawn out of thehydrate formation vessel 120 continuously. As a result, water pocketsmay build up in the hydrate, and where hydrate amalgamates sufficiently,water will not drain through it because it will not be permeable enough.Therefore, draining as much free water from the system as possible viathe collector pipes 146 ensures the greatest efficiency with respect tothe overall amount of water used and the amount of hydrate formed. (Itwill also ensure that the smallest amount of water remains afterdecontamination activities stop, which water adds dead weight to thehydrate formation vessel and may impede handling.)

[0039] Once water spray is established and the injection-recovery systemis charged, water that does not form hydrate and that drains from thevessel 120 is collected and recycled. Recycling system control 130 firstrecharges the water injection system 124 with water that has beencollected at the bottom of the hydrate formation vessel 120; therefore,water is not dumped or disposed of on site, which would be undesirablesince that water may contain dissolved fractions of the toxic gases. Asgas hydrate continues to form, water is consumed at a rate on the orderof not less than about 0.8 cubic meter of water for each cubic meter ofhydrate (varying depending upon the particular hydrate). Therefore,water is drawn from a local source of water 122 by input pump 123 andfed into the injection system 124. (Because gas hydrates can form fromdifferent types of water including polluted, brackish, or saline water,the nature of the input water is essentially unimportant so long as itis cool enough or can be chilled enough for the gas hydrate to form.)Chiller 119 chills the input water to temperatures required for hydrateto form spontaneously. Where gas hydrate forms rapidly, the heat ofexothermic formation of the hydrate will also need to be removed (e.g.,by chilling) so that the pressure/temperature field within the hydrateformation vessel does not vary to the point that hydrate formation isretarded.

[0040] When a hydrate formation and storage vessel is filled with asmuch hydrate as can be contained, it is detached from the intermediatestage pressure vessel 114 and the air exhaust assembly 140. Pressure ismaintained on the upstream supply of air containing the toxic gas to thehydrate formation vessel 120 by one-way valves on the intake housing,which allows the intake assembly 108 to be rapidly attached to anddetached from a succession of hydrate formation and storage vesselswhile maintaining pressure conditions of hydrate stability within thevessel 114. Pressure is maintained on the downstream, exhaust assembly140 by closing an air release valve assembly, which meters the exhaustair during the hydrate formation process to keep pressure within thehydrate formation vessel within the range required for hydratestability. The hydrate formation vessel 120 is detached from the airintake 108 at its quick release junction 116, from the exhaust assembly140, and from the water injection and recycling system 142, and anotherhydrate formation vessel 120 is fitted in its place. One-way valves 144that are self-sealing upon removal of the water injection system 124 andwater collection and drain system 128 allow the flexible water piping tobe quickly detached from and fixed to successive tanks without allowingpressure within the hydrate formation vessel 120 to drop to a levelwhere the toxic gas hydrate would become unstable in a very short periodof time.

[0041] As shown in FIG. 1, the detachable valve system 144 is externalto the pressure vessel 120. In another mode, the one-way detachablevalves can be contained within the vessel, and connection may be byquick-fit insertion of a male plug for water injection 124 and drain 128systems into a female socket in the pressure vessel at the base of thedrain pipe 146.

[0042] Water remaining after the vessel is filled with as much hydrateas possible is left in the pressure vessel. When the hydrate is causedto dissociate by heating and/or lowering the pressure in the vesselafter it has been removed from the toxic air collection system, thewater released by the hydrate mixes with the excess water. The water andthe hydrate-forming gas released upon dissociation of the hydrateseparate naturally, whether the gas is in gaseous or liquid form (asdetermined by contolling the pressure and temperature in the vessel),and stratify by density. For example, if chlorine is the toxic gas beingdecontaminated and pressure (less than ten atmospheres) and temperaturein the vessel are controlled to maintain the chlorine in liquid formafter the hydrate dissociates, the liquid chlorine will be less densethan water and will float on the water. Although some mixing will occurwhen the fluid is being drawn from near the boundary between the twoliquids, the two substances can be removed separately by draining intoindustry standard tanks for safe removal. If it is not used to form morehydrate during seququent decontamination, the remainingchlorine-saturated water can be nutralized by a number of simple means,e.g., by mixing it with sodium hydroxide, which causes the chlorine toform common table salt, NaCl. The concentrated toxic gas/liquid can thenbe removed from the pressurized vessel in which the hydrate has beenfrom from the contaminated air. When the toxic gas and water have beenremoved, the hydrate formation vessel can be reused.

[0043] According to another embodiment of apparatus for practicinghydrate-based decontamination, toxic gas hydrate decontamination unitscan be fixed in place and brought into operation in a decontaminationemergency. Where it can be anticipated that toxic gas attack terrorismis either very likely or likely to cause a large number of deaths ordisruption, locations such as major government buildings, subwaysystems, and closed sports arenas can have permanently installed toxicgas hydrate decontamination units installed therein. Such fixed unitsare similar in construction to the previously described embodiment, butare constructed in accordance with their fixed nature rather than a needfor portability. For instance, intake pipes can be built into thebuilding either in a fixed manner or put in place in such a way thatthey can be replaced following a decontamination incident with a minimumamount of effort, but without the extreme flexibility and ease ofhandling that are a part of the portable intake pipe assembly describedabove.

[0044] Because it is known or anticipated beforehand where the greatestnumber of people are likely to be (for instance, in the seats of acovered sports arena), the intakes can be located so as to ingest airthat has been contaminated by toxic gas in such a way that it isingested from the likely areas that toxic gas may be released so thatthe toxic gas/air mix is drawn away from the people. Likewise, theexhaust assembly is built into the building to vent processed air to theoutside of the building or insulation to be cleared.

[0045] A built-in apparatus for diverting toxic air from the location ofthe largest number of people in a building or other construction willalso provide an element of protection even where the air contains gasesthat are not suitable for capture using hydrate formation. Many of theother toxic gases that are likely to be used by terrorists can betreated at least in part by being passed through a toxic gas hydrateformation unit since water—especially under mild pressure—can rapidlyhydrolyze or hold in solution many of these other potentially hazardousand toxic gases.

[0046] Permanently installed gas hydrate decontamination units shouldhave their air intake systems linked with building or installationventilation systems. These can be designed to draw contaminated air awayfrom personnel and into the decontamination units. Because thehydrate-forming gas is the airborne toxic gas itself, only water needsto be supplied to the apparatus.

[0047] Where permanent installations are established, the maximumanticipated size of a toxic gas hazard must be estimated and thedecontamination units engineered accordingly so that a spill can beprocessed entirely with the installed equipment, unless provision ismade for the easy exchange of hydrate formation vessels as in the caseof portable apparatus as described above. In a sealed building fromwhich personnel have been evacuated, however, it is feasible to operatethe decontamination units through more than one cycle. In other words,when the hydrate storage tanks become filled, they may be processedthrough dissociation to allow the gas and water to be recovered. The gasmay be safely stored in as concentrated and as pure a form as possibleto reduce the toxic volume, and the water can be reused in subsequentcycles of hydrate formation and dissociation until decontamination iscomplete. The contaminated water is then disposed of in a manner similarto that with a portable apparatus.

[0048] An example of such a permanently installed hydrate-baseddecontamination apparatus as installed, for instance, in a subwaystation is illustrated in FIG. 3. Because toxic gases that are likely tobe used in a terrorist incident in such a confined space, e.g.,chlorine, are heavier than air, air collection systems can be installedat a low level within the confined space. An air collection system usingstandard metal or plastic pipe 204 can, for instance, be placed beneaththe lip 206 of the station platform 202 or in a flat pipe below the edgeof the platform where there is insufficient “indentation” below the edgeof the platform. The intakes can be spaced relatively close together, asillustrated by intakes 212, or relatively farther apart, as illustratedby intakes 214, depending on the likely density of people above or thelocal air volume to be processed. Internal constrictors (not shown) areprovided, which are industry standard inserts into the airpipe or intakeorifice that force the air to pass through an airspace in theconstrictor that is smaller than the pipe in which it is inserted andthus reduce the air that can be inducted by particular intakes 212, 214.This allows for even or preferential intake of air regardless of thedistance of a particular intake from the intake pump or fan. Thecollection system may also be placed at “ground” or track level, or asecond, lower collection system may be placed below a “lip” installationto facilitate capture of all the gas and especially that which hasdescended to below the level of the platform where people will belocated. Providing for a collection system nearly at, but just below,the platform level, however, will provide for best removal of anyreleased gas from the immediate vicinity of the people. Embedded vents218 may also be provided in the surface of the platform 202 to draw airand gas into the decontamination apparatus.

[0049] Contaminated air from the collection system 204 is drawn into apermanently installed hydrate fixation system 220, which can beactivated automatically by means of sensors or manually either locallyor from a remote location such as a disaster control room. The hydratefixation system is shown as placed upon the platform 202 for simplicityof illustration, although actual installations may be built within anenclosure within the platform or into the walls of the enclosed space. Acompact air pressurization and chilling system combined with a waterspray injection system in a configuration similar to that in theapparatus illustrated in FIG. 1 and described above captures andcompresses the toxic material in the form of gas hydrate. Purified airfrom which the toxic agent has been removed is exhausted to the surfacevia conduit 226 in a permanent ventilation system. The air collectionsystem generates slightly negative pressure within the confined space sothat fresh air enters the confined space, e.g., through passenger orother access passages 228. Thus, people exiting the confined space willbe moving toward a fresh air influx, which is beneficial to their escapefrom the contaminated air and to their survival.

[0050] According to a further embodiment of apparatus according to theinvention, certain locations or environments can themselves bepressurized and chilled, if necessary, in their entirety so that toxicgas and liquid suitable for forming gas hydrates can be converted to gashydrate upon the introduction of water in situ, i.e., without thehydrate-forming gas or liquid having to be drawn into any of theapparatus described above. For example, a tunnel in which a toxichydrate-forming substance has been released (e.g., by a leaking orcrashed truck carrying a large load of liquid chlorine that isevaporating as the liquid chlorine leaks from the truck) can be sealedat both ends along with all airshafts and ventilation apparatus so thatmoderately elevated pressures can be generated and maintained within thetunnel. Thus, the tunnel can be isolated.

[0051] Once isolated, the tunnel is pressurized and chilled as necessaryso that the toxic gas or liquid will spontaneously form gas hydrate uponthe introduction of water into the tunnel. This can be done, forinstance, by robotic equipment or by personnel suitably protected toenter the toxic gas hazard area. Once the toxic gas and/or liquid hasbeen converted to hydrate, it is chemically inert and can be collectedas a solid material in a number of fashions. Ideally, it is placed inhydrate dissociation tanks (that can be similar to the above-describedhydrate formation/dissociation vessels) and allowed to dissociate incontrolled fashion to release the constituent water and gas of thehydrate. The gas and water then naturally separate, and the toxic gasand water can be concentrated under safe conditions as previouslydescribed.

[0052] Another embodiment of apparatus according to the invention is aportable, in-situ containment structure (chemical hazard containmentstructure) that is similar to an inflatable dome fabricated fromairtight, artificial fabric. The dome is large enough to contain anentire vehicle such as a bus or rail car from which toxic gas/liquid hasbeen spilled or is leaking. The structure must be strong enough tomaintain the slightly elevated pressures required to allow gas hydrateto form. Ideally, it would be rapidly deployed around the situs of therestricted chemical hazard incident; water spray would be injected; andthe toxic gas rendered harmless in the form of gas hydrate so that itcould be removed to dissociation apparatus and the gas and waterrecovered as previously described.

[0053] Thus, as described above according to the invention, toxic gaseshaving relatively small molecules (e.g., less than about 7 Å diameter)that form sI and sII hydrates are captured and removed from contaminatedair by directly compressing the gases and the atmospheric air in whichthey are borne in the presence of water. Additionally, hydrates of toxichydrate-forming materials are formed directly from liquids of toxicgases (e.g., liquid chlorine) because the toxic gases will spontaneouslyform hydrates in the presence of water under appropriate temperature andpressure conditions.

[0054] Where toxic gases having molecules that are too large to permitformation of sI or sII hydrates are dispersed in air, simply bringingthe toxic gas and the atmospheric air to pressure and temperatureconditions suitable for forming gas hydrate of the particular toxic gaswill not cause hydrate of the toxic gas to form. That is because asubstantial percentage of both the smaller and larger voids in the gashydrate must be filled by gas molecules of appropriate size in order tostabilize the gas hydrate crystalline lattice, but the large toxic gasmolecules are too large to fill the voids in sI or sII hydrates or tofill the small voids in sH hydrates and other large hydrates with veryasymmetrical (i.e., different diameter) voids. Thus, the water moleculelattice will not form gas hydrate in that situation.

[0055] Such larger-molecule toxic agents may, however, be captured andbound up in type sH hydrate by using a “companion agent” or “companiongas” to stabilize the hydrate lattice. The companion agent is a gasother than the larger-molecule toxic agent, the molecules of which aresmall enough (less than about 7 Å) to fill the smaller voids in sHhydrate. The larger molecules of the toxic agent (greater than about 7Å) occupy the larger voids in the hydrate crystal, and the latticethereby remains stable. Thus, toxic agents having relatively largemolecules can also be captured using hydrate to decontaminate an area inwhich such larger-molecule toxic agents have been released.

[0056] The companion gas may be a single species of gas such asessentially pure carbon dioxide, chlorine, hydrogen sulfide or methane(which are known to participate in forming sH type hydrate), or amixture of gases. Ideally, the companion gas is non-toxic and chemicallyinert, such as some of the hydrocarbon gases and/or carbon dioxide, butit may itself be a toxic gas such as chlorine. The presence of chlorine,in particular, allows the larger-molecule toxic gas to be incorporatedinto sH gas hydrate at relatively low pressures (on the order of threeatmospheres) and high temperatures (on the order of twenty five degreesCelsius), and chlorine is available at relatively low cost. This has thebenefit of allowing much more rapid and less costly sequestration of thelarge molecule toxic gases.

[0057] In addition to using this method to separate and sequesterlarger-molecule toxic gas from air, the method may also be applied toliquids in which such toxic gases are dissolved. When a suitablecompanion gas and either water or water vapor is passed through a fluidcontaining the dissolved, large-molecule toxic materials underappropriate conditions of temperature and pressure, gas hydrate willform.

[0058] When the gas hydrate forms, it extracts the toxic agent from thefluid in which it is dissolved and incorporates it into the large voidsof the solid hydrate. The hydrate is then separated from the fluid bybuoyancy or other separation processes and is brought to a hydrateconcentration vessel, as described above in the context ofsmaller-molecule toxic gases, where it is washed or otherwise purifiedof residual fluid while it is a stable solid hydrate. The fluid may beeither toxic or non-toxic and is handled and disposed of appropriately,separate from the toxic hydrate. The toxic hydrate may be safely storedin the hydrate form, where it is chemically inert. Because the toxic gasis compressed when incorporated in gas hydrates (by a factor estimatedto be on the order of about 30 as compared to the volume the gas wouldoccupy at ambient atmospheric temperature and pressure for some sHhydrates), the toxic gas will occupy a relatively small volume. Suchsafely “stored” toxic gas may not be as compressed as would be the caseif the toxic gas were stored in liquid form; however, storage of thesetoxic gases in the form of gas hydrates may be safer than storage solelyin pressurized containers containing gas, liquid, or a mixture thereof.

[0059] Once the larger-molecule toxic gas hydrate has been formed andcollected using methodology as described above in connection withsmaller-molecule toxic gas hydrate, it may be allowed to dissociate in acontrolled fashion by means of which the toxic gas can be gathered andcondensed. Dissociation of the toxic gas hydrate may, in fact, provide acontrollable method not only for gathering toxic agents, but also fordetoxifying these materials (both larger-molecule andsmaller-molecule)—particularly nerve agents.

[0060] Nerve agents are lethal organo-phosphorous compounds. Over twothousand different related species have been identified, and theseinclude many insecticides. The two major types of nerve agents arenon-persistent (G-agents) and persistent (V-agents). The non-persistentgroup of nerve agents is volatile and mainly a vapor hazard wheninhaled. The persistent group of nerve agents is generally nonvolatileand mainly a liquid exposure hazard to the skin or eyes. V-agents (VX,etc) are known to be up to ten times more poisonous than the G-agents.TABLE 3 Examples of types of nerve agent groups Name Code Name ChemicalStructure Non-persistent Tabun GA (CH₃)₂N—P(═O)(—CN)(—OC₂H₅) Sarin GB(CH₃)—P(═O)(—F)(—OCH(CH₃)₂) Soman GD (CH₃)—P(═O)(—F)(—OCH(CH₃)C(CH₃)₃)Cyclohexyl GF (CH₃)—P(═O)(—F)(cyclo-C₆H₁₁) methylphosphonoflouridatePersistent O-ethyl S- VX (CH₃)—P(═O)(—SCH₂CH₂N[CH(CH₃)₂]₂)(OC₂H₅)diisopropylaminomethyl methylphosphonothiolate

[0061] Many of these agents are soluble in water. For instance, thenerve agents Sarin and Soman both hydrolyze, thereby changing chemicalstructure and becoming non-toxic except for some reaction products. Forinstance, hydrogen fluoride (HF), which is itself toxic but can behandled safely and disposed of, and phosphoric acid, which isessentially non-toxic in dilute mixtures, are produced as a result ofthe hydrolization. In addition, mustard agent is also slightly solublein water and hydrolyzes slowly, thereby producing the acid hydrogenchloride (HCl), which is not urduly toxic in weak to moderateconcentrations. A prime reactant to detoxify these materials throughsimple chemical reactions is water, through a process of hydrolysis, andthe water and gas mixture produced when hydrate is dissociated may beoptimal to promote these chemical reactions that break down the nerveagents. Thus, it will be appreciate that first forming hydratefacilitates hydrolysis by efficiently “gathering” the toxic agent in thehydrate.

[0062] Upon formation of the toxic gas hydrate, the toxic molecules aredispersed in a framework of water molecules, with each individual toxicmolecule surrounded by numerous water molecules. When the hydratedissociates, each molecule of toxic gas is surrounded by watermolecules. This natural mixing of toxic gas molecules and liquid waterin the dissociation product is highly effective to increase the rate ofhydrolysis of the toxic molecules-during and immediately followingdissociation. Reaction of water with the toxic gas causes a chemicalreaction that changes the original toxic gas molecule and renders itessentially harmless and is presently one of the main means ofdecontaminating these agents. Thus, not only may toxic material becaptured and rendered harmless once incorporated within hydrates, butdissociation of those same toxic material-containing hydrates mayintroduce an efficient process of hydrolysis that chemically detoxifiesthe toxic material.

[0063] Portable apparatus 300 for decontaminating an area in which alarger-molecule toxic agent has been released is illustrated in FIG. 4.The apparatus may be generally identical to that illustrated in FIGS. 1and 2, and components of the apparatus illustrated in FIG. 4 that areidentical or generally similar to components illustrated in FIG. 1 arelabeled similarly but in the 300's instead of the 100's. The portableapparatus for decontaminating larger-molecule toxic agents by means ofgas hydrate illustrated in FIG. 4 differs from the apparatus illustratedin FIG. 1 primarily to the extent that a companion gas or companionagent conduit 356 is provided. Preferably, the companion gas conduit 354provides companion or helper gas 359 to the intermediate pressure vessel314, i.e., upstream of the main, hydrate formation pressure vessel 320,so that the companion gas is pressurized and can participate in hydrateformation as quickly and efficiently as possible. The apparatus 300shown in FIG. 4 operates and is used in generally the same manner asdescribed above in connection with the portable apparatus illustrated inFIG. 1, with the additional provision of providing a helper or companiongas or agent.

[0064] Furthermore, apparatus for decontaminating larger-molecule toxicagents via hydrate formation can be installed on a permanent basis,e.g., as part of the ventilation system of a building as illustrated inFIG. 3 for smaller-molecule toxic agent decontamination apparatus.

[0065] The apparatus 300, it will be appreciated, is also suitable forforming smaller-molecule gas hydrate, as described above. In the case ofsmaller-molecule toxic gases that spontaneously form sI or sII gashydrate, injecting a non-toxic companion gas into the inflowingcontaminated air 309 will not affect the formation of the toxic gashydrate, and it (the companion gas) will be expelled from the apparatusalong with the decontaminated air 348.

[0066] The foregoing detailed description has been provided merely toillustrate the principles of the present invention and is not intendedto be limiting. To the contrary, the present invention is intended toencompass all substitutions, modifications, and equivalents within thespirit and scope of the appended claims.

1-24. (Cancel)
 25. Apparatus for decontaminating an area in which atoxic, hydrate-forming agent has been released, said apparatuscomprising: a relatively light-weight, portable containment vessel, saidcontainment vessel being pressurizeable and constructed of waterproofmaterials; a water spray distribution system disposed within saidcontainment vessel for spraying water into the interior of saidcontainment vessel; and a toxic agent intake system, said toxic agentintake system comprising one or more light-weight, collapsible intakeconduits and a pump system configured to draw said toxic agent into saidone or more conduits and deliver said toxic agent into said containmentvessel.
 26. The apparatus of claim 25, further comprising a companiongas injection conduit configured to introduce a companion gas into saidapparatus to be mixed with said toxic agent.
 27. The apparatus of claim25, further comprising means for cooling said containment vessel. 28.Integrated air circulation and toxic agent decontamination apparatus,comprising: air circulation ducting disposed within a building or otherarea in which people gather; a pressurizeable containment vessel incommunication with said air circulation ducting; and a water spraydistribution system disposed within said containment vessel for sprayingwater into the interior of said containment vessel.
 29. The apparatus ofclaim 28, further comprising a companion gas injection conduitconfigured to introduce a companion gas into said apparatus to be mixedwith said toxic agent.
 30. The apparatus of claim 28, further comprisingmeans for cooling said containment vessel. 31-59. (Cancel)